Graphite is widely used in fiber draw furnaces due to its high operational temperature. In the hot zone of the furnace, reactions with the furnace wall cause erosion and formation of saturated SiC and SiO vapor. This saturated vapor is cooled as it moves lower in the furnace and away from the hot zone which results in deposition of SiC on the furnace wall. In addition SiO precipitates out and forms SiO particles. These particles typically agglomerate into larger particles which may eventually break loose from the draw furnace wall, get reintroduced into the gas stream and contact the fiber. Large graphite and SiO particles can cause fiber breaks when they adhere to the fiber and create flaws on its surface. Smaller graphite particulate that becomes incorporated into the fiber during the draw process may cause unacceptable product losses due to draw-induced point defects.
In addition to causing defects in the draw furnace, particulate can be transported out of the draw furnace and into a slow-cooling device due to momentum diffusion from the fiber motion. Due to the small diameter of the slow-cooling treatment device (SCD), these particles are in close proximity to the fiber and may cause additional point defects and fiber breaks as the fiber is still hot and therefore vulnerable to damage. In addition, equipment and process changes may contribute to increased number of particulates that flow into the SCD and increase the potential of breaks.